Spinal stabilization is one approach to alleviating chronic back pain caused by displaced disk material or excessive movement of individual vertebrae. Conventional stabilization techniques include fusing two or more vertebrae together to circumvent or immobilize the area of excessive movement. Normally, the vertebral disk material which separates the vertebrae is removed and bone graft material is inserted in the space for interbody fusion. In addition to or in place of the bone graft material, a spinal implant may be inserted in the intervertebral space.
The conventional surgical approach for stabilization has been posteriorly for ease of access to the spine and to avoid interfering with internal organs and tissue. Usually the implant site is prepared to maintain natural lordosis and to accept a certain sized implant within certain pressure limits. This requires considerable time and skill by the surgeon.
U.S. Pat. No. 5,653,763 discloses an orthopaedic cage device having a rectangular cross-section and an intervertebral space shape conforming structure formed of two opposing shell elements being hinged at one end to form an interior volume therebetween. A threaded shaft is axially disposed in the interior volume and is held in place by a retaining ring slideably mounted at the non-hinged axial end of the device. A nut, being of substantially the same dimension as the maximum cross-section of the interior volume in its initial disposition, is disposed on the threaded shaft such that rotation of the shaft causes the nut to translate axially within the interior volume. This translation causes the nut to engage the tapered surface of the interior volume, which in turn causes the non-hinged end of the device to spread such that the device conforms to the natural space between the vertebral bones and provides for the proper curvature of the spine.
U.S. Pat. No. 6,821,298 discloses a fenestrated, hollow intervertebral cage containing a packed, harvested bone graft for fusing adjacent vertebrae together while maintaining or correcting the angular alignment and balance of the spine. Use of the device for an anterior interbody fusion results in a fused bone segment having a predetermined fixed angular orientation. The apparatus has a cage unit adjustably coupled to an expansion cap, and an adjustable wedge to support the adjacent vertebrae with facing surfaces at a predetermined angle relative to each other. A connecting bolt may be threaded or fixed to the rear of the cage unit.
U.S. Pat. No. 6,562,074 discloses a spinal insert which can be manipulated to adjust the height of the implant through links connected to the upper and lower plates.
U.S. Pat. No. 6,120,506 discloses a lordotic implant and a tap for use in preparing the vertebrae. The implant is designed to be inserted between the non-parallel end plates of adjacent vertebrae and maintain the natural lordotic angle of the spine. This is done through the use of a threaded tapered plug inserted in a tapped hole in the direction required by the lordosis of the spine. The implant is hollow and has radial apertures for accommodating bone graft material.
U.S. Pat. No. 6,015,436 discloses a tubular spinal implant. The implant is hollow and has radial apertures for interbody fusion through bone growth material. The device is placed between adjacent vertebrae with the opposite ends of the tube contacting the opposing vertebrae. The opposite ends are threaded together to form the hollow tube.
U.S. Pat. Nos. 7,211,112; 7,850,733; and 8,273,129 disclose opposing wedge ramps having a main body having upper and lower sections with mating sidewalls relatively movable along an inclined ramp. The inclined ramp forms a wedge movable between inclined sidewalls of the main body sections. The main body sections and the inclined ramp form a hollow cube-shaped structure with common open sides.